A jet of water with a cross-sectional area a is striking against a wall at an angle $\mathrm{\theta }$ to the horizontal and rebounds elastically. If the velocity of water jet is v and the density is $\rho$, the normal force acting on the wall is

• A

  $2{\mathrm{av}}^2\mathrm{\rho } \cos \mathrm{\theta }$

• B

  ${\mathrm{av}}^2\mathrm{\rho } \cos \mathrm{\theta }$

• C

  $2\mathrm{av} \mathrm{\rho } \cos \mathrm{\theta }$

• D

  ${\mathrm{a}}^2\mathrm{v\rho } \cos \mathrm{\theta }$